全文获取类型
收费全文 | 877篇 |
免费 | 36篇 |
国内免费 | 3篇 |
专业分类
化学 | 590篇 |
晶体学 | 6篇 |
力学 | 20篇 |
数学 | 81篇 |
物理学 | 219篇 |
出版年
2023年 | 2篇 |
2022年 | 24篇 |
2021年 | 31篇 |
2020年 | 15篇 |
2019年 | 19篇 |
2018年 | 21篇 |
2017年 | 15篇 |
2016年 | 32篇 |
2015年 | 32篇 |
2014年 | 35篇 |
2013年 | 54篇 |
2012年 | 53篇 |
2011年 | 70篇 |
2010年 | 56篇 |
2009年 | 49篇 |
2008年 | 43篇 |
2007年 | 46篇 |
2006年 | 33篇 |
2005年 | 31篇 |
2004年 | 27篇 |
2003年 | 11篇 |
2002年 | 24篇 |
2001年 | 20篇 |
2000年 | 20篇 |
1999年 | 15篇 |
1998年 | 15篇 |
1997年 | 9篇 |
1996年 | 7篇 |
1995年 | 5篇 |
1994年 | 7篇 |
1993年 | 10篇 |
1992年 | 6篇 |
1991年 | 7篇 |
1990年 | 8篇 |
1989年 | 4篇 |
1988年 | 3篇 |
1986年 | 5篇 |
1985年 | 3篇 |
1984年 | 2篇 |
1983年 | 3篇 |
1982年 | 3篇 |
1981年 | 6篇 |
1980年 | 6篇 |
1979年 | 3篇 |
1978年 | 4篇 |
1977年 | 4篇 |
1976年 | 3篇 |
1974年 | 2篇 |
1973年 | 4篇 |
1924年 | 2篇 |
排序方式: 共有916条查询结果,搜索用时 15 毫秒
811.
812.
Marta M. Andrade 《Tetrahedron》2004,60(41):9235-9243
The direct O-formylation of two selectively protected sugar derivatives using the Vilsmeier-Haack (V-H) complex POCl3·DMF was studied. Primary O-TBDMS and O-TBDPS ethers of sucrose, the most common disaccharide, underwent regio and chemoselective O-formylation with this formylating agent. This conversion was also studied with a monosaccharide analogue. 相似文献
813.
The adsorption of (1) bovine serum albumin in acetate buffer, (2) albumin followed by glutaraldehyde crosslinking, (3) albumin followed by exposure to an albumin/glutaraldehyde solution, and (4) albumin after the surface was subjected to treatment (3), has been studied using Ta oxide/Ta chips and SiO2/Si wafers as substrates. The films were washed, air dried and measured in air using an automatic laser ellipsometer, 6328 Å. The films formed from treatment (3) and treatment (4) have a lower refractive index and are thicker than films formed from treatment (1) and treatment (2). The adsorption of albumin on SiO2/Si wafers seems to be slower than that on the Ta oxide/Ta surfaces. 相似文献
814.
Lee Y Andrade JS Buldyrev SV Dokholyan NV Havlin S King PR Paul G Stanley HE 《Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics》1999,60(3):3425-3428
We study traveling time and traveling length for tracer dispersion in two-dimensional bond percolation, modeling flow by tracer particles driven by a pressure difference between two points separated by Euclidean distance r. We find that the minimal traveling time t(min) scales as t(min) approximately r(1.33), which is different from the scaling of the most probable traveling time, t* approximately r(1.64). We also calculate the length of the path corresponding to the minimal traveling time and find l(min) approximately r(1.13) and that the most probable traveling length scales as l* approximately r(1.21). We present the relevant distribution functions and scaling relations. 相似文献
815.
A broad chemometric study was made on structural data from non-fused and non-pi-complexed pentafulvenes obtained both from the Cambridge structural database (CSD) and from several studies to synthesise new fulvene compounds. Three main differentiated pentafulvene groups can be established considering bond distances extracted from the CSD database. Structural data for the new 1-mono and 1,4-disubstituted 2,3,6-trioxypentafulvenes and 1,4-disubstituted-6-amino-2, 3-dioxypentafulvenes reveal different structural behaviours due to their high functionality. The chemometric techniques employed comprise principal component analysis, cluster analysis, selection of essential variables (Procrustes rotation) and isoprobability curves, all of them giving essentially the same general chemical conclusions. 相似文献
816.
M. M. Piñeiro B. E. de Cominges J. L. Legido S. García-Garabal M. López M. I. Paz Andrade 《Journal of Thermal Analysis and Calorimetry》1998,52(3):799-814
Studies were previously made of the excess molar enthalpies, Hm
E, at 298.15 K and normal atmospheric pressure of the ternary mixtures (ethyl propanoate or 3-pentanone) + (n-hexane) + (n-decane,
n-dodecane or n-tetradecane) and (1-propanol) + (3-pentanone) + (n-hexane, n-heptane, n-octane, 1-hexanol or 1-heptanol).
In the present work, experimental values of Hm
E were correlated through use of the Cibulka and Nagata equations, and a new correlation equation is proposed. Experimental
data were compared with the predictions of the UNIFAC I (version of Tassios), UNIFAC II (version of Larsen) and Nitta-Chao
group contribution models. Hm
E values were used to test several empirical predictive methods, both symmetric (Kohler, Jacob-Fitzner, Colinet and Knobeloch-Schwartz),
and asymmetric (Tsao-Smith, Toop, Scatchard, Hillert and Mathieson-Tynne).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
817.
Carlosena A Prada D Andrade JM López P Muniategui S 《Analytical and bioanalytical chemistry》1996,355(3-4):289-291
The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with L'vov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment). 相似文献
818.
A method is presented for the detection and determination of hydrogen sulfide. It is based on the selective and reversible adsorption of hydrogen sulfide on the surface of a piezoelectric crystal coated with a cadmium iodide/urea/-glycerol solution. The proposed detector has a response time of 30 s with linear response over the concentration range 2–25 μl l?1 (ppm). 相似文献
819.
Classification of edible vegetables affected by different traffic intensities using potential curves
Heavy metals in soils have largely been used to evaluate the impact of motorised traffic in the vicinity of motorways. Also in this field of work it is of paramount importance to analyse the vegetables grown in these areas since their consumption is one of the main sources of metal intake by people; not in vain human food is directly or indirectly derived from plants. Accordingly, a set of edible vegetable samples were first analysed and, then, classified employing different multivariate chemometric techniques; among them, SIMCA and a simplified mode of potential curves. The analytical variables were selected after a comprehensive study of roadside soil pollution where Pb, Cd and Cu were found to be the main metallic pollution tracers. Different groups of vegetables were obtained which were explained as a function of both the agricultural conditions (private versus commercial) and the different traffic intensities supported by the cultivated areas. 相似文献
820.
A. Carlosena D. Prada J. M. Andrade P. López S. Muniategui 《Fresenius' Journal of Analytical Chemistry》1996,355(3-4):289-291
The need to determine micronutrients and toxic elements in soils has grown in recent years and cadmium is of special interest. A method has been developed for the determination of cadmium in soils based on a prior acid digestion of the samples with nitric acid in closed Teflon vessels, into a microwave over. The cadmium determination was carried out by graphite furnace atomic absorption spectrometry (GFAAS) with Lvov platform. Optimum operating conditions, analyte modifiers and matrix interferences have been investigated. The best matrix modifier was found to be ammonium dihydrogen phosphate. The interferences are greatly reduced under these operating conditions and calibration can be performed with simple aqueous solutions of the metal standard. The method is rapid and provides accurate and precise results that agree with certified values for two reference materials: BCR 141 (calcareous loam soil) and BCR 277 (estuarine sediment). 相似文献